1.Field of the Invention
The present invention generally relates to the field of gas stream scrubbing technology. More particularly, the present invention relates to a method and an apparatus for maintaining inlet duct lines of scrubber units free from clogging due to accumulation of particulates and the like.
2.Description of the Related Art
It is common in the treatment of industrial waste gas streams to integrate a cleaning apparatus downstream (relative to the direction of waste flow) of a processing system. The function of the cleaning apparatus is to receive and process effluents produced in upstream process operations.
For example, in the semiconductor manufacturing industry, numerous integrated cleaning systems are commercially available and oftentimes employed for treating effluents and off-gases from semiconductor manufacturing processes. Semiconductor manufacturing processes may include chemical vapor deposition, metal etching, and etch and ion implantation operations. Examples of commercial integrated gas stream cleaning systems include the Delatech Controlled Decomposition Oxidizer, the Dunnschicht Analagen System Escape system, and the Edwards Thermal Processing Unit. Each of these systems include a thermal processing unit for oxidative decomposition of effluent gases, combined with a wet quench for temperature control of off-gases from a hot oxidation section, and wet scrubbing systems for a removal of acid gases and particulates found in the oxidation process.
Scrubbers, like the ones employed above, generally include elongated columns that accommodate effluents and subject them to a counter-current contacting with liquid solvents, reactant solutions, or slurries. The result of the counter-current contacting is an intimate mixing which assists the absorption process to effect removal of impurities from the effluents.
Integrated cleaning systems may be built into the manufacturing system to be an integral part of the manufacturing system. In contrast, stand-alone systems are maintained in a housing structure independent from the process or manufacturing system. Although such stand-alone units may be integrated to the process of the upstream equipment, stand-alone units enjoy a greater degree of mobility than their integrated cleaning system counterparts.
Use of scrubber technology is not limited to integrated cleaning systems but may also be incorporated in stand-alone operation systems. Examples include: a) unheated chemically reacting packed bed dry scrubbers, b) unheated chemisorptive packed bed dry scrubbers, c) heated chemically reacting packed bed dry scrubbers, d) heated catalytically reacting packed bed dry scrubbers, e) wet scrubbers, and f) flame-based thermal treatment units. Each of the aforementioned units is applicable to selected usages depending on the nature of the gas stream undergoing treatment.
Use of scrubber technology is accompanied by various deficiencies, including particulate clogging of the scrubber inlets, lines and manifolds. A line and/or manifold that is even partially clogged prevents the efficient flow of process gases therethrough. Partially clogged lines or manifolds could also interfere with the absorption processes occurring with the normal operations of a scrubber, e.g., dissolution of a gaseous component or components in a solvent medium.
In application to scrubbing of effluent gas streams, various causes for clogging of scrubbers have been suggested. Clogging can be caused by the reaction of silicon bearing in-coming species reacting with water, or water vapor, and depositing droplets of silicon-containing water in the inlet of a scrubber. This clog-formation mechanism is present for processes applied to semiconductor tools used for epitaxial growth on wafers and which tend to use trichloro silane and dichloro silane. Clogging can also be caused by the condensation deposition of condensable species in the inlet section to a water scrubber. Clogging may also be caused by the back-migration of water vapor from a water scrubber into the incoming process line. This back-migrating water vapor can then react with incoming species and form materials with low volatility and result in their depositing in the inlet to a water scrubber. This last mechanism is, for example, characteristic of scrubber abatement of tools for the metal etch process.
During metal etching machining, e.g., an off-gas such as BCl.sub.3 (boron trichloride) may be produced. BCl.sub.3 reacts with water vapor to form a non-volatile particulate boric acid which condenses, accumulates, and at least partially clogs inlet ports or inlet lines.
Existing practice has several methods to attempt to eliminate these types of clogs. One method attempts to flush the clog periodically with water. This subjects the clog to a pressurized water stream that dissolves the clog and the clog is flushed away. An undesirable effect of the flushing process is, however, the back migration of water will now originate from the point of introduction of flush water and result in increased hydrolysis reactions upstream with other water sensitive gases, such as WF6 (tungsten hexafluoride), and merely cause the clog to move further upstream.
Another method utilizes the introduction of a mechanical plunger mechanism or other solid removal means to keep the inlet and lines free of solids accumulations. However, such mechanical solutions are costly, labor-intensive, require significant maintenance and are susceptible to mechanical breakdown.
It is therefore an object of the present invention to provide an improved method and apparatus for cleaning scrubber manifold lines so as to reduce the tendency for clog formation in the lines, the scrubber inlets and the manifolds.
It is another object of the present invention provide such an apparatus and method which prevents the back-migration of process water.
It is another object of the present invention to prevent hydrolysis reactions and minimize particulate accumulation.
It is still another object of the present invention to provide method and apparatus of the above-described type which has minimal interference with the operation of the scrubber.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.